1. Field of the Invention
The invention pertains to the use of non-copolymerizable hydroperoxides of the general formula Rxe2x80x94Oxe2x80x94Oxe2x80x94H as regulators in the free-radically initiated polymerization of ethylenically unsaturated monomers.
2. Background Art
Free-radical initiators or free-radical initiator combinations are used for initiating the polymerization of ethylenically unsaturated monomers. If the molecular weight of the resulting polymers is to be reduced to a desired value, it is usual to employ regulators in addition to the initiator. Customary regulators are, for example, mercaptans such as mercaptopropionic acid, 2-mercaptoethanol, 2-mercaptopropanol, mercaptoacetic acid, tert-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan and tert-dodecyl mercaptan. Further examples of regulators are hydroxylammonium salts such as hydroxylammonium sulfate; organic solvents such as toluene, diethylbenzene and xylene; halogenated solvents such as chloroform; formic acid; sodium bisulfite; and alcohols such as methanol. A disadvantage of these regulators is that mercaptans and halogenated hydrocarbons have a strong odor and are of concern from a toxicological point of view. Furthermore, both mercaptans and halogenated hydrocarbons are difficult to remove from the polymer dispersion formed.
U.S. Pat. No. 3,800,007 describes the bulk, solution, emulsion and suspension polymerization of xcex1, xcex2-unsaturated monomers using alkyl- or cycloalkyl-substituted cumene peroxides. The cumene peroxides are used in the temperature range of from xe2x88x9210xc2x0 C. to 70xc2x0 C. as auxiliaries for preparing peroxide-functional graft and block copolymers in a first step. In a second step, in the temperature range of from 80xc2x0 C. to 150xc2x0 C., the peroxide groups then decompose and initiate the graft or block copolymerization with further comonomers.
WO-A 95/30697 describes the use of organic peracids Rxe2x80x94COxe2x80x94Oxe2x80x94Oxe2x80x94H as regulators in polymerization reactions. The peracid is added in addition to a standard initiator in the polymerization, with the initiators being selected so that the polymerization takes place at a temperature below the decomposition temperature of the regulator.
WO-A 91/07440 discloses copolymerizable allyl hydroperoxides as regulators in polymerization processes. The objective was to provide reactive crosslinkable macromonomers for moldings and coatings. Owing to the bifunctionality of these molecules in having both an unsaturated group as well as a peroxidic group, polymers with bifunctional end groups which can subsequently be reacted by polymer-analogous reactions to provide epoxide functions are produced. The allyl hydroperoxides become fixed constituents of the polymer chain, thus altering the properties of the polymer, which is generally not desired. The copolymerizable allyl hydroperoxides also influence (slow) the polymerization behavior of the other monomers. Depending on the respective reactivities, the result can be different polymer compositions which in turn produce unique polymer properties.
It is an object of the invention to provide substances which are suitable for regulating the molecular weight in polymerizations and which can also be used without an additional initiator system, for simultaneously initiating the polymerization and regulating the molecular weight.
The invention provides for the use of non-copolymerizable hydroperoxides of the general formula Rxe2x80x94Oxe2x80x94Oxe2x80x94H as regulators in the free-radically initiated polymerization of ethylenically unsaturated monomers, where R is H, a C1-C18-alkyl radical, a C7-C22-aralkyl radical or a saturated or unsaturated carbocyclic or heterocyclic ring having from 3 to 18 carbon atoms. The hydrocarbon radicals R may be substituted or unsubstituted.
The radical R may be unbranched or branched and may be substituted by one or more substituents selected from the group consisting of halogen, hydroxy, alkoxy, aryloxy, epoxy, carboxyl, ester, amido, nitrile and keto groups. Preferred radicals R are, in addition to hydrogen, isopropyl, tert-butyl, tert-pentyl, 1,1-dimethylbutyl, and 1,1-dimethylpentyl radicals, each of which may be further substituted by an OH group. A preferred aralkyl radical is the cumene radical. As carbocyclic radicals, preference is given to the menthol and pinene radicals.
Particular preference is given to hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, tert-pentyl hydroperoxide, 1,1-dimethylbutyl hydroperoxide, 1,1-dimethylpropyl hydroperoxide, 1,1-dimethyl-3-hydroxybutyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, p-menthyl hydroperoxide, pinanyl hydroperoxide, 1-methylcyclopentyl hydroperoxide, 2-hydroperoxy-2-methyltetrahydrofuran, 1-methoxycyclohexyl hydroperoxide, 1,3,4,5,6,7-hexahydro-4a(2H)-naphthalenyl hydroperoxide, xcex2-pinene hydroperoxide, and 2,5-dihydro-2-methyl-2-furanyl hydroperoxide.
The non-copolymerizable hydroperoxides can be used as regulators in conjunction with an initiator system. In a preferred embodiment, the hydroperoxides are used simultaneously as regulator and initiator without further free-radical initiators being employed. In general, the amount of hydroperoxide is from 0.01 to 15% by weight, preferably from 0.1 to 5% by weight, particularly preferably from 0.5 to 3% by weight, in each case based on the total weight of monomers.
As monomers, it is possible to use one or more monomers selected from the group consisting of vinyl esters of unbranched and branched alkylcarboxylic acids having from 1 to 18 carbon atoms; acrylic esters and methacrylic esters of branched and unbranched alcohols and diols having from 1 to 18 carbon atoms; ethylenically unsaturated monocarboxylic and dicarboxylic acids, their amides and N-methylolamides and nitriles; ethylenically unsaturated sulfonic acids; ethylenically unsaturated heterocyclic compounds; dienes; olefins; vinylaromatics; and vinyl halides.
Suitable vinyl esters are those of carboxylic acids having from 1 to 12 carbon atoms. Preference is given to vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of xcex1-branched monocarboxylic acids having from 9 to 11 carbon atoms, for example VeoVa9R or VeoVa10R (trade names of Shell). Particular preference is given to vinyl acetate.
Suitable monomers from the group consisting of acrylic esters and methacrylic esters are esters of unbranched or branched alcohols having from 1 to 15 carbon atoms. Preferred methacrylic esters and acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate, t-butyl acrylate and 2-ethylhexyl acrylate.
Examples of suitable ethylenically unsaturated monocarboxylic and dicarboxylic acids and their amides, N-methylolamides, and nitriles, are acrylic acid, methacrylic acid, fumaric acid, maleic acid, acrylamide, N-methylolacrylamide, N-methylolmethacrylamide, and acrylonitrile. Examples of ethylenically unsaturated sulfonic acids are vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Suitable ethylenically unsaturated heterocyclic compounds are N-vinylpyrrolidone and N-vinylpyridine.
Preferred vinylaromatics are styrene, methylstyrene and vinyltoluene. The preferred vinyl halide is vinyl chloride. Preferred olefins are ethylene and propylene, and preferred dienes are 1,3-butadiene and isoprene.
If desired, from 0.1 to 5% by weight, based on the total weight of the monomer mixture, of auxiliary monomers can additionally be copolymerized. Preference is given to using from 0.5 to 2.5% by weight of auxiliary monomers. Examples of auxiliary monomers are ethylenically unsaturated monocarboxylic and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid and maleic acid; ethylenically unsaturated carboxamides and nitriles, preferably acrylamide and acrylonitrile; monoesters and diesters of fumaric acid and maleic acid, e.g. the diethyl and diisopropyl esters, and also maleic anhydride, ethylenically unsaturated sulfonic acids or their salts, preferably vinylsulfonic acid or 2-acrylamido-2-methylpropane sulfonic acid. Further examples are precrosslinking comonomers such as multiply ethylenically unsaturated comonomers. Examples include divinyl adipate, diallyl maleate, diallyl phthalate, allyl methacrylate and triallyl cyanurate. Post-crosslinking comonomers may also be used, for example acrylamidoglycolic acid (AGA), methyl methylacrylamidoglycolate (MMAG), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylolallylcarbamate, alkyl ethers such as the isobutoxy ethers or esters of N-methylolacrylamide, N-methylolmethacrylamide, or N-methylolallylcarbamate. Also suitable are epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate. Further examples include silicon-functional comonomers such as acryloxypropyltri(alkoxy)silanes and methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, the alkoxy groups being, for example, ethoxy and ethoxypropylene glycol ether radicals. Mention may also be made of monomers containing hydroxy or CO groups, for example hydroxyalkyl esters of methacrylic acid and acrylic acid, e.g. hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, and also compounds such as diacetoneacrylamide and acetylacetoxyethyl acrylate or methacrylate.
Particular preference is given to monomers selected from vinyl acetate, vinyl esters of xcex1-branched monocarboxylic acids having from 9 to 11 carbon atoms, vinyl chloride, ethylene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, styrene, and mixtures thereof. The greatest preference is given to mixtures of vinyl acetate with ethylene; of vinyl acetate, ethylene and a vinyl ester of an a-branched monocarboxylic acid having from 9 to 11 carbon atoms; of n-butyl acrylate with 2-ethylhexyl acrylate and/or methyl methacrylate; of styrene with one or more monomers selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; and of vinyl acetate with one or more monomers selected from methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and optionally ethylene. The aforesaid mixtures may further comprise one or more auxiliary monomers.
The choice of comonomers and their relative proportions by weight is preferably made so that a glass transition temperature (xe2x80x9cTgxe2x80x9d) from xe2x88x9250xc2x0 C. to +120xc2x0 C., more preferably from xe2x88x9230xc2x0 C. to +95xc2x0 C., results. The glass transition temperature Tg of the polymers can be determined in a known manner by means of differential scanning calorimetry (DSC). The Tg can also be calculated approximately in advance by means of the Fox equation. According to T. G. Fox, BULL. A, PHYSICS SOC. 1, 3, page 123 (1956): 1/Tg=x1/Tg1+x2/Tg2+ . . . +xn/Tgn, where xn is the mass fraction (% by weight/100) of the monomer n and Tgn is the glass transition temperature in Kelvin of the homopolymer of the monomer n. Tg values for homopolymers are given in Polymer Handbook 2nd Edition, J. Wiley and Sons, New York (1975).
The free-radically initiated polymerization of the ethylenically unsaturated monomers can in principle be carried out using all polymerization methods known for this purpose, e.g. bulk polymerization, solution polymerization, precipitation polymerization, suspension polymerization and emulsion polymerization. Preference is given to solution, suspension and emulsion polymerization. Greatest preference is given to suspension and emulsion polymerization.
The polymerization temperature is generally from 40xc2x0 C. to 100xc2x0 C., preferably from 60xc2x0 C. to 90xc2x0 C. The copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene or vinyl chloride may optionally be carried out under superatmospheric pressure, generally from 5 bar to 100 bar. The initiation of the polymerization can be carried out using the customary water-soluble or monomer-soluble initiators or redox initiator combinations. Examples of water-soluble initiators are the sodium, potassium and ammonium salts of peroxodisulfuric acid, hydrogen peroxide, t-butyl peroxide, potassium peroxodiphosphate, t-butylperoxopivalate, cumene hydroperoxide, isopropylbenzene monohydroperoxide, asobisisobutyronitrile. Examples of monomer-soluble initiators are dicetyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dibenzoyl peroxide, Trigonot, t-butylper-2-ethylhexanoate and t-butylperpivalate. These initiators are generally used in an amount of from 0.01 to 10.0% by weight, preferably from 0.1 to 0.5% by weight, in each case based on the total weight of monomers. As redox initiators, use is made of combinations of the abovementioned initiators with reducing agents. Suitable reducing agents are the sulfites and bisulfites of the alkali metals and of ammonium, for example sodium sulfite, the derivatives of sulfoxylic acid such as zinc or alkali metal formaldehyde sulfoxylates, for example sodium hydroxymethanesulfinate, and ascorbic acid. The amount of reducing agent is generally from 0.01 to 10.0% by weight, preferably from 0.1 to 0.5% by weight, in each case based on the total weight of monomers. In a preferred embodiment, no further free-radical initiators are added apart from the non-copolymerizable hydroperoxide.
In the preferred processes of suspension and emulsion polymerization, the polymerization is carried out in the presence of surface-active substances such as protective colloids and/or emulsifiers. Suitable protective colloids are, for example, partially saponified polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl acetals, starches, celluloses and their carboxymethyl, methyl, hydroxyethyl and hydroxypropyl derivatives. Suitable emulsifiers include anionic, cationic and nonionic emulsifiers, for example anionic surfactants such as alkyl sulfates having a chain length of from 8 to 18 carbon atoms, alkyl or alkylaryl ethers sulfates having from 8 to 18 carbon atoms in the hydrophobic radical and up to 60 ethylene oxide or propylene oxide units, alkylsulfonates or alkylarylsulfonates having from 8 to 18 carbon atoms, esters and monoesters of sulfosuccinic acid with monohydric alcohols or alkylphenols, or nonionic surfactants such as alkyl polyglycol ethers or alkylaryl polyglycol ethers having up to 60 ethylene oxide or propylene oxide units.
It is possible for all the monomers to be charged initially, all of them to be metered in or part of them to be charged initially and the remainder to be metered in after initiation of the polymerization. The metered additions can be carried out separately (in space and in time), or all or some of the components to be metered in can be metered in preemulsified form.
It is possible for all of the hydroperoxides used as regulators to be charged initially, all of them to be metered in or part of them to be charged initially and the remainder to be metered in. If the hydroperoxides are used only as regulators and in combination with an initiator, it is possible for all of the hydroperoxide to be charged initially, or all of it to be metered in together with monomer or initiator, or part of it to be charged initially and the remainder to be metered in together with monomer or initiator. In those process variants in which all or part of the hydroperoxide is metered in, preference is given to metering in the hydroperoxide regulator in a molar ratio of more than 0.2:1 to the initiator in the initiation of the polymerization. This metering rate can be increased as desired during the course of the polymerization.
If the hydroperoxides are used both as regulator and as initiator, all of the hydroperoxide is charged initially, or all of it is metered in together with monomer, or part of it is charged initially and the remainder is metered in together with monomer, and the reducing agent is in each case metered in. The hydroperoxide is particularly preferably initially charged or metered in in such amounts that the molar ratio of hydroperoxide to reducing agent is from 1.2:1 to 20:1, preferably from 1.5:1 to 7.5:1.
After the polymerization is complete, residual monomers and volatile components can be removed by means of after-polymerization, distillation, stripping with inert gas or a combination of these measures. To produce polymer powders which are redispersable in water, the aqueous dispersions can, after addition of protective colloids as atomizing aids, be spray dried in a known manner.
The polymers which are obtainable by use according to the invention of hydroperoxide regulators can be used in the applications typical for such polymers, for example in building chemicals, if desired in combination with hydraulic binders such as cements (Portland cement, alumina cement, pozzolanic cement, slag cement, magnesia cement, phosphate cement), plaster of Paris, water glass, for the production of building adhesives, in particular tile adhesives and insulating adhesives, plasters and renders, knifing fillers, flooring screeds, self-spreading compositions, sealing slurries, jointing mortars and paints. They can also be used as binders for coating compositions and adhesives or as coating compositions and binders for textiles, fibers, wood and paper.